La4(Si5.2Ge2.8O18)(TeO3)4 and La2(Si6O13)(TeO3)2: Intergrowth of the lanthanum(III) tellurite layer with the XO4 (X=Si/Ge) tetrahedral layer

Two novel lanthanum(III) silicate tellurites, namely, La4(Si5.2Ge2.8O18)(TeO3)4 and La2(Si6O13)(TeO3)2, have been synthesized by the solid state reactions and their structures determined by single crystal X-ray diffraction. The structure of La4(Si5.2Ge2.8O18)(TeO3)4 features a three-dimensional (3D) network composed of the [(Ge2.82Si5.18)O18]4− tetrahedral layers and the [La4(TeO3)4]4+ layers that alternate along the b-axis. The germanate–silicate layer consists of corner-sharing XO4 (X=Si/Ge) tetrahedra, forming four- and six-member rings. The structure of La2(Si6O13)(TeO3)2 is a 3D network composed of the [Si6O13]2− double layers and the [La2(TeO3)2]2+ layers that alternate along the a-axis. The [Si6O13]2− double layer is built by corner-sharing silicate tetrahedra, forming four-, five- and eight-member rings. The TeO32− anions in both compounds are only involved in the coordination with La3+ ions to form a lanthanum(III) tellurite layer. La4(Si5.2Ge2.8O18)(TeO3)4 is a wide band-gap semiconductor.